The present invention relates to an optical method and to an optical device which uses a laser source for nonintrusively measuring the temperature in a flowing liquid.
Temperature measurement devices based on a laser source are known. For example, European Patent Application No. 345188 discloses a device which operates based on the observation of interference fringes created within a flowing fluid in a pipe. These observations are made at the output of two optical fibers which transport light from an external laser source. The disclosed apparatus is satisfactory for such situations, but does require intrusion in the fluid being studied, something that is not always possible.
Various nonintrusive techniques for measuring the parameters of a fluid (for example, temperature or pressure) are already known. For example, French Patent Application 2,579,320 discloses an ultrasonic wave measurement method which is intended for the thermal monitoring of nuclear reactors. The disclosed technique allows only a single parameter of the fluid to be measured, namely, its temperature.
The main drawback of presently known nonintrusive temperature measurement devices is their excessively long response time. In difficult situations, such as measurement of the temperature of droplets, in a spray for example, where the measured volume changes due to evaporation over time during measurement, in liquid-gas two-phase flow, in the measurement of the temperature field in a plane, and in the measurement of temperature in a turbulent flow, such measurement remains difficult, if not impossible to carry out. Also, there are difficulties in obtaining an apparatus that has a short response time and which disturbs the flow as little as possible.